FOLIAGE-LEAVES AND THE CHLOROPHYLL FUNCTION. 539 
Effect of an Atmosphere free from CO,.— The seedlings grown 
in small pots were placed inside the apparatus for a period of 
30 to 40 days. The leaves which, at the beginning of the ex- 
periment, were emerging from the sheathing scale, exposing a 
tip 1:5 to 2 em. in length, attained a length of 15 cm. and a 
complete normal expansion, corresponding to that of organs 
grown in the open air. Such leaves usually attain a length of 
20 to 30 em. by a slow process of growth lasting several months, 
and my experiment therefore covers only the earlier stages of 
development. 
Effect of Darkness.—Specimens placed in a dark chamber 
during a period of from 30 to 40 days exhibited an exaggerated 
elongation of the cotyledonary and leaf-scales, as well as the leaf 
itself, which retained its lamina in the plicately folded position. 
The increase in length amounted to 20 to 30 per cent. more than 
in control plants. 
Comment.—The development of seedlings of Zea and Phenix 
may proceed so long as the necessary amount of plastic material 
is available. In Zea the amount is sufficient to allow a normal 
development for a period of 10 to 12 days, and in Phenix for a 
much longer period. 
INTERPRETATION OF EXPERIMENTAL RESULTS. 
The first and most apparent conclusion to be drawn from a 
consideration of my own and other experiments, is that the leaves 
of different species exhibit individual reactions to an atmosphere 
free from CO,. For the better comprehension of such reactions, 
it will be found convenient to divide the existence of the leaf 
into three periods, instead of two as has been done by Vóchting. 
The first includes the growth and development of the leaf from 
a rudimentary condition to the unfolding of the lamina, corre- 
sponding to a similar period outlined by Vóchting. The second 
includes the unfolding and expansion of the lamina to such 
extent as to attain a normal stature; and the third includes the 
existence of the organ after maturity has been reached. A 
disregard of the conditions attendant on the two last-named 
periods has led to the formulation of eontradictory conclusions 
from the use of the same material in the hands of different 
investigators. 
All the plants hitherto examined by myself and others with 
respect to the relation of the leaves to the air have been shown 
